Date of this Version
The purpose for this study is threefold. All involve single handed lifting tasks where the height of the lifted object, the distance of the lifted object from the body, and the angle of the lift relative to the body were varied. First, examine the activity of each of the shared musculature of selected shared muscles between the shoulder and cervical spine. Second, attempt to empirically model the activations of the shared muscles. Third, to understand the relationship between the active and antagonistic contraction. Finally, to establish a biomechanical model to estimate the compressive forces on the cervical spine.
Ten subjects participated in the study and performed lifting of five different weights from twenty different locations. Those locations were a combination two heights, two reach distances, and five different angles. EMGs activities of three selected muscles of the shared musculature between the neck and shoulder were the dependent measures. The independent variables were height, distributing angles, weights, gender, and reach distance. The muscles chosen were the Upper Trapezius, Stemocleidomas and Levator Scapula.
Results showed that muscles on both the left and right side of the neck were very active during these right hand lifts. The antagonistic contractions in all the muscles studied were found to be related to the contractions happening in the active counterpart of the muscle. Results also showed that the activation pattern in all active muscles is predictable based on hand loads, arm posture, and anthropometric measurements. In addition, it was found that work height, reach distance, gender, and distributing angles are all significant factors in stimulating activation in the shared muscles. Finally, it was found that the co-contraction is accurately predicted by the active contraction for the same muscles in the left and the right side respectively.
Examination the balance of moment produced during lifting tasks at the C4/C5 disc was conducted and it was found that the active shared muscles and their co-contracting counterparts are the main contracting muscles. Utilizing these findings, a biomechanical model was constructed that was capable for estimating the compressive forces on the cervical spine at C4/C5 vertebra, due to hand usage.
Advisor: Jeffery C. Woldstad